I did some additional testing and it looks like, surprisingly, some files play well, eg:
/usr/share/sounds/freedesktop/stereo/camera-shutter.oga /usr/share/sounds/speech-dispatcher/dummy-message.wav whereas others, if not most, cause problems, eg: /usr/share/sounds/freedesktop/stereo/phone-incoming-call.oga /usr/share/sounds/purple/send.wav PS. Sorry for bad formatting of my previous email. I didn't spot it being sent as html. -- Pozdrawiam / Regards, Orzech